The present invention generally relates to an improved process for the production of a protein isolate from a vegetable protein material such as an oilseed meal which not only is highly efficient and simple to practice on a commercial scale, but provides a protein isolate with an improved degree of whiteness.
Protein isolates derived from vegetable protein sources such as the oilseeds, typically soybeans, cottonseed and the like, have contributed substantially to the economic importance of these vegetable protein materials as a crop. The isolates derived from oilseeds in particular have proven to be a useful nutritional supplement in a variety of foods and beverages and with further processing have been suitably texturized to simulate a variety of natural protein foodstuffs such as meat and cheese. A protein isolate can be generally characterized as a product resulting from the extraction, subsequent concentration and purification of proteinaceous material from a proteinaceous source such as a vegetable protein or oilseed material. Typically, the protein isolate on a moisture free basis will have a protein content which will range between about 90 and 98% by weight after isolation of the protein from the nonproteinaceous and cellular material present in most types of vegetable protein material.
A conventional procedure for the isolation of protein from a vegetable protein material such as an oilseed meal or flakes, comprises as the first step, removing soluble lipids or oil from the vegetable protein material either by means of a mechanical apparatus such as an expeller or by solvent extraction with aliphatic hydrocarbons such as hexane. The resulting material obtained from solvent extraction of the oilseed or vegetable protein source is commonly referred to as defatted oilseed meal and is normally in the form of flakes which will still contain many ingredients including complex and varying types of proteins, sugars, fibers, etc. The protein and sugars are then dissolved out of the flakes by dispersing the flakes in an aqueous bath and preferebly adding a food grade alkaline material to raise the pH of the mixture to above about 6.5 to expedite removal of the protein. Typical alkaline materials include sodium, potassium, or calcium hydroxide. The resultant liquor containing the dissolved proteins and sugars is then separated from undissolved solids either by passing the mixture through a screen or by centrifugation.
The clarified liquor is then reduced in pH to between about 4.0 to 5.0 in order to lower the pH in the mixture to near the isoelectric point of the protein. Reduction of pH is achieved by the addition of an acidic reagent such as a mineral or organic acid. The protein immediately begins to precipitate from the solution as a "curd". Thereafter centrifugation or filtration is carried out in order to concentrate the curd to a solids level of between about 20 and 30% by weight, and at this time the "mother liquor" or "whey" is separated from the precipitated protein which is in the form of a curd. At this point of the process, the protein curd while being entirely functional in a wide variety of food applications, is not considered to possess the best color since undesirable materials remain entrapped in the precipitated protein giving it a "yellowish" cast and further processing is normally required to provide an isolate with a light enough color to be suitable for use in some food products. Therefore, in the prior art the curd obtained from acid precipitation of the alkaline extract of the soy flakes was reslurried in water after which additional centrifugation or separation of the protein was carried out in order to remove any entrapped undesirable components which effected the color. Repeated washing of the precipitated curd with water was believed to be necessary in order to substantially improve the whiteness of the resultant curd since it seems logical that additional washing would remove a larger percentage of entrapped material. It has been recognized, however, that while repeated washings of the curd with either water, alcohols or mixtures thereof results in a slight improvement in whiteness, nevertheless, repeated processing of this type reduces the overall efficiency of the isolation process since a certain percentage of the protein is lost during each washing step thereby reducing the yield. Furthermore, alcohol washing reduces the solubility of the protein source. Additionally, large quantities of whey are discarded with each washing.
A basic breakthrough was made in the instant invention by considering ways and alternatives which would simplify the conventional process for the production of a protein isolate from a vegetable protein material and in so doing it was unexpectedly discovered that not only could the process be simplified to a great extent but an isolate could be obtained which was much whiter in color than isolates which underwent far more extensive processing techniques.
This unexpected improvement in whiteness was achieved by heating the precipitated curd to a critically defined temperature range of about 115.degree.-145.degree. F. preferably about 130.degree. to 135.degree. F. followed by concentration of the curd to a solids level exceeding about 44% by weight. Concentration of the solids to such a level not only improves the yield and efficiency of the process but causes an unexpected improvement in whiteness of the isolate.
The noted temperature range is critical relative to obtaining the necessary level of solids of at least about 44% by weight to improve the economy and yield of the process. Certainly it is apparent that concentration to a high solids level with result in a more efficient and economical process although the improvement in whiteness by concentration to the noted minimum solids level was entirely unexpected.
It is, therefore, an object of the present invention to provide an improved process for the production of a protein isolate from a vegetable protein source.
It is also an object of the present invention to provide an improved process for the production of a protein isolate which is economical and reliable to practice on a commercial scale.
It is a further object of the present invention to provide a process for the production of a protein isolate which has a satisfactory degree of whiteness and hence functionality in a variety of food products.
It is also an object of the present invention to provide a process for the production of isolates from a vegetable protein source wherein a high yield of protein in the isolation process is obtained.